This invention relates to a method of treating liquid wastes containing heavy metal chelate compounds.
Since liquid wastes discharged from plants for manufacturing printed circuit boards or the like contain heavy metal chelates such as Cu-EDTA derived from chemical copper plating solutions, if the liquid wastes are discharged as they are into rivers or other water bodies, they may cause circumstantial pollution. Various methods of treating these liquid wastes have hitherto been put to practical use. For example, there have been known relatively effective treating methods such as an excess calcium hydroxide addition method of adding calcium hydroxide to liquid wastes containing Cu-EDTA chelates to adjust pH to 12 or more and then adding a flocculant thereby causing flocculating precipitation, an oxidative separation method of treating Cu-EDTA by using a powerful oxidizer and an adsorption method of treating Cu-EDTA by means of ion exchange resins or the like.
Heavy metals in the liquid wastes can be removed more or less by thesetreating methods. However, the excess calcium hydroxide addition method requires much chemical cost and, in addition, causes scalings to pumps and pipeways and cloggings in the filter. The oxidative decomposition method requires a longer processing time to attain a sufficient removal rate even when the solution is warmed. The adsorption method requires a high regeneration of ion exchange resins or the like and no effective improvement can be expected for the Cu-removal rate (refer to Patent KOKUKU (Post-Exam Publn) No. 25280/1982).